An apparatus has heretofore been developed and proposed to successively make plastic bags each of which includes side gusset portions and a zipper portion incorporated into superposed two layers of panel portion, as disclosed in Japanese Laid-Open Patent Publication No. 010055 of 2004. In the apparatus of the publication, webs of panel material are superposed into two layers and fed longitudinally thereof. A sheet of side gusset material is folded into halves and supplied to extend widthwise of the webs of panel material. A web of zipper material is supplied to extend longitudinally of the webs of panel material, the sheet of side gusset material and the web of zipper material being interposed between the layers of panel material. In addition, the layers of panel material are heat sealed with the web of zipper material longitudinally of the webs of panel material by longitudinal seal means after the sheet of side gusset material and the web of zipper material are interposed. The layers of panel material are then heat sealed with each other longitudinally of the webs of panel material by longitudinal seal means so that a longitudinal sealed portion can be formed longitudinally of the webs of panel material. The layers of panel material are further heat sealed with the sheet of side gusset material widthwise of the webs of panel material by cross seal means so that cross sealed portions can be formed widthwise of the webs of panel material. Accordingly, the plastic bag includes the side gusset portions formed by the sheets of side gusset material and the zipper portion formed by the web of zipper material, which are incorporated into the layers of panel portion formed by the webs of panel material. The plastic bag further includes a top edge formed by the longitudinal sealed portion and side edges formed by the cross sealed portions.
An apparatus has also been proposed to successively make plastic bags each of which includes side gusset portions and a bottom gusset portion, as disclosed in Japanese Laid-Open Patent Publication No. 254984 of 2000. In the apparatus of the publication, in addition to the sheet of side gusset material extending widthwise of the webs of panel material, a web of bottom gusset material extends longitudinally of the webs of panel material, the sheet of side gusset material and the web of bottom gusset material being interposed between the layers of panel material. The layers of panel material are heat sealed with the web of bottom gusset material longitudinally of the webs of panel material by longitudinal seal means so that longitudinal sealed portions can be formed longitudinally of the webs of panel material. The layers of panel material are heat sealed with the sheet of side gusset material widthwise of the webs of panel material by cross seal means so that cross sealed portions can be formed widthwise of the webs of panel material. Accordingly, the plastic bag includes the side gusset portions formed by the sheets of side gusset material and the bottom gusset portion formed by the web of bottom gusset material, which are incorporated into the layers of panel portion formed by the webs of panel material. The plastic bag further includes a bottom edge formed by the longitudinal sealed portions and side edges formed by the cross sealed portions.
By the way, the apparatus is recently requested to successively make plastic bags each of which has a tall structure and includes side gusset portions and a zipper or bottom gusset portion. However, in the apparatus of the publications, the sheets of side gusset material extend widthwise of the webs of panel material. In addition, the layers of panel material are heat sealed with the sheet of side gusset material widthwise of the webs of panel material by the cross seal means so that the cross sealed portions can be formed widthwise of the webs of panel material. The plastic bag includes the side edges formed by the cross sealed portions. The plastic bag therefore has a height in a direction which is not longitudinal but widthwise of the webs of panel material. In this connection, the webs of panel material have to be wide to successively make plastic bags each of which has a tall structure. However, it is difficult in the apparatus to use the webs of panel material which are wide. For example, in general, the webs of panel material are fed longitudinally thereof by feed rollers and through guide rollers. In this case, the feed and guide rollers are required to have lengths corresponding to the widths of webs of panel material which are wide, to be problematic in rigidity.
In addition, in the apparatus, a web of panel material may be supplied from a single roll and slit along the centerline thereof to be divided into two webs of panel material, the webs of panel material being then superposed into two layers, as described in Japanese Laid-Open Patent Publication No. 158057 of 2001. The web of panel material may have a pattern printed thereon before being slit. In this case, the webs of panel material can then be superposed into two layers after being slit without resulting in discrepancy in pattern between the layers of panel material. However, this method cannot be applied to the plastic bag having a tall structure by reason that the web of panel material is too wide before being slit. Accordingly, the webs of panel material have to be supplied from two rolls and superposed into two layers, resulting in difference in extension between the layers of panel material. The difference is accumulated gradually, resulting in discrepancy in pattern between the layers of panel material.
It is therefore an object of the invention to provide an apparatus which can successively make plastic bags each of which has a tall structure and includes side gusset portions incorporated into superposed layers of panel portion without using webs of panel material which are wide.